This invention is generally directed to carrier and developer compositions, and more specifically the present invention relates to specific carrier compositions formulated from fly ash; and wherein the carrier particles have an average diameter of greater than 44 microns. In one embodiment of the present invention, therefore, carrier and developer compositions are obtained from fly ash, which compositions when incorporated into xerographic imaging and/or printing apparatuses enable images of excellent resolution; that is, with substantially no background, an absence of dark, undesirable bands appearing thereon, and substantially no adverse bead carryout.
Additionally, in another specific embodiment of the present invention, undesirable fly ash generated by the burning coal is subjected to classification, and dry magnetic separation wherein there results specific spherical carrier particles useful in electrostatographic imaging systems. The aforementioned developer compositions, and particularly the spherical carrier components thereof are obtained in a simple and economical manner thereby enabling in most instances low cost developer compositions in comparison to those compositions obtained in many of the prior art processes.
The formation and development of xerographic latent images generated on photoconductive devices by electrostatic means is well known, one such method involving the formation of an electrostatic latent image on the surface of a photoreceptor. This photoreceptor is generally comprised of a conductive substrate containing on its surface a layer of photoconductive insulating material; and in many instances a thin barrier is situated between the substrate and photoconductive layer for the purpose of preventing undesirable charge injection. The latent image generated on the photoconductive member can be developed by a composition comprised of toner particles and carrier particles. The carrier particles generally consist of various materials, inclusive of those which may contain a coating thereon. Thus, there can be selected as carriers those described in U.S. Pat. No. 3,767,578, which illustrates developer mixtures containing nodular carrier beads having a number size average distribution in the range of 50 to 1,000 microns. Examples of carrier beads disclosed in this patent include metals such as steel, copper, nickel, ceramics, or glasses. According to the disclosure of the '578 patent, ceramic or brass carrier particles can be prepared from a wide variety of magnetic or nonmagnetic refractory oxides including silicon, aluminum, iron oxide, nickel oxide, and the like. In one embodiment the carrier substances of this patent are prepared by agglomerating small particles with known granulating or pelletizing procedures, preferably in the presence of a resinous binder. The agglomerates are heated for the purpose of providing hardness and strength to the carrier particles. Specifically, it is indicated in U.S. Pat. No. 3,767,578 that one useful method for preparing carrier particles involves mixing a particulate carrier material with a binder, and charging the mixture to an inclined rotary mixing plate over which is sprayed a liquid to affect the wetting of the particles. As the mixing plate rotates the agglomerates continue to grow. The largest agglomerates are directed to the surface and roll off at the ascending side of the lower edge of the mixing plate. The smaller agglomerates remain on the rotary plate until they become larger. By variation of the angel of inclination of the rotary plate, the periphery velocity, the location of the charging area within which the material is introduced into the rotary plate, and the height of the peripheral edge of the rotary plate, the size range of the resulting agglomerates can be adjusted to within close tolerances.
Also, there is illustrated in U.S. Pat. No. 4,125,667 a process for preparing high surface area ferromagnetic carrier materials wherein the materials have been classified enabling a specific surface area of at least about 150 cm.sup.2 per gram, a particle size volume distribution wherein the geometric standard deviation is less than about 1.3, and a particle size distribution with an average particle diameter of less than about 100 microns. Suitable classification methods disclosed in this patent include air classification, screening, cyclone separation, centrifugation, and combinations thereof.
Additionally, in U.S. Pat. No. 3,939,086, there is described a method for obtaining highly classified steel carrier cores by mechanically separating round particles from irregularly shaped beads through controlled vibration, such as a vibrating table set at a predetermined slope. It is indicated in this patent that raw low carbon hypereutectoid steel beads when received from the manufacturer are generally not satisfactory as electrostatographic carrier cores since they usually contain at least about 30 percent by weight of nonround materials. Apparently, the raw steel beads are manufactured by a rotating electrode process, or atomized from an electric arc furnace melt; and although spherical particles are produced, mixtures of round and irregular shaped particles generally result from these processes. It is known that nonround particles are generally undesirable since they contain slag, hollow particles, chipped particles, and flat particles, which cause variations in electrostatic carrier density resulting in carrier beads sticking to electrostatic drum surfaces thereby causing print deletions, scratches on the photoreceptor surface, and nonuniformity of triboelectric properties in the developer mixture. A similar disclosure is contained in U.S. Pat. No. 3,849,182.
Moreover, there is disclosed in U.S. Pat. No. 3,769,053 processes for the treatment of fly ash enabling iron concentrate products with from about 45 to about 65 percent by weight of iron, reference column 3, beginning at line 35. The specific steps for obtaining the products of the '053 patent are outlined in column 2, beginning at line 5. However, the specific particles obtained in accordance with the teachings of the '053 patent have several disadvantages associated therewith including that most of the particles have an average diameter of less than 44 microns, and therefore are not very useful as carrier particles in xerographic imaging systems. Specifically, thus the particles prepared in accordance with the '053 patent when incorporated, for example, into xerographic imaging systems as part of a xerographic developer composition permitted in images with undesirable bands thereon; and further, with the aforementioned compositions, bead carrout occurs. Moreover, the magnetic particles formulated in accordance with the teachings of the '053 patent, and in particular particles obtained by the process of working Example I, possess characteristics that prevent in most instances their utilization in electrostatographic imaging systems in that, for example, images of low resolution, including those with undesirable bands thereon, are obtained. Specifically, thus the particles obtained in accordance with the process of Example I of the '053 patent contain 56.5 percent by weight of iron, have a saturation magnetization of 53 electromagnetic units per gram (emu/gram), and an apparent density of 2.2 grams/cm.sup.3. Furthermore, magnetic particles obtained in accordance with the process of Example III contained 57.2 percent by weight of iron, have a saturation magnetization of 51 emu/gram, and an apparent density of 2.2 grams/cm.sup.3.
Moreover, there is disclosed in U.S. Pat. No. 4,319,988 a specific process for the separation of high grade magnetite from fly ash by adhering to specific process steps, reference column 7, beginning at around line 19. Specifically, thus there are obtained in accordance with the teachings of the '988 patent magnetites from fly ash which are useful, for example, in the cleaning of coals. However, there is no teaching in this patent with respect to obtaining carrier particles, particularly those that have an average diameter of greater than 44 microns.
Although magnetic particles produced by some of the processes described are generally suitable for their intended purposes, there continues to be a need for improved processes for preparing and obtaining carrier particles. Additionally, there continues to be a need for a simple, economically attractive process for obtaining carrier particles suitable for use in developer compositions. Additionally, there continues to be a need for specific spherical carrier particles, particularly those resulting from fly ash; and wherein the particles obtained can, subsequent to coating, be incorporated into developer mixtures useful for permitting the development of latent electrostatic images. Moreover, there continues to be a need for the formulation of spherical carrier particles from waste fly ash. Also, there continues to be a need for iron oxide carrier particles which have an apparent density of at least 2.2 or equal to or greater than 2.4 grams/cm.sup.3, thus resulting in particles of high purity enabling their use for incorporation into xerographic developer mixtures. There also is a need for carrier particles that are of low density and low magnetic moment enabling the use of a softer and less abrasive brush system in electrostatographic imaging processes.
There is also a need for spherical magnetic carrier particles useful in xerographic imaging apparatuses, which particles have an average particle diameter of greater than 44 microns, a magnetic moment of from about 60 to about 70 electromagnetic units per gram, and an apparent density greater than 2.4 grams/cm.sup.3 ; or which carrier particles have a magnetic moment of from about 50 to about 70 electromagnetic units per gram and a density of from about 2.2 to about 2.5 grams/cm.sup.3.